Neat poly(aryl ether ketone)s such as neat polyetheretherketones (PEEKs), offer a good balance of technical properties, including a very high melting point, excellent thermal stability and chemical resistance (including environmental stress cracking resistance), good ductibililty and processability, high strength, high stiffness and high impact resistance (as characterized by a standard ASTM notched Izod test).
However, for certain demanding applications, a still higher level of strength, stiffness and impact resistance is required which cannot be achieved by neat poly(aryl ether ketone)s.
It has already been found that the desired level of strength and stiffness can be obtained by adding a fibrous filler such as glass fiber to the neat poly(aryl ether ketone). However, such fiber-reinforced poly(aryl ether ketone)s still suffer from the same limitation in impact resistance as that of neat poly(aryl ether ketone)s.
It has also already been found that the desired level of strength and impact resistance can be achieved by neat polyarylenes; because of their outstanding intrinsic strength, similar to that of fiber-reinforced polymers, these neat polyarylenes are often referred to as “self-reinforcing polymers”. However, the stiffness of such neat polyarylenes is still not as high as needed in certain demanding applications, although being somewhat higher than that of neat poly(aryl ether ketone)s. Besides, neat polyarylenes suffer from several other important limitations: they have no ductile break, they are difficult to process at the molten state and they have a somewhat lower thermal stability and chemical resistance than polyaryletherketone(s).
Fiber-filled polyarylenes have been incidentally disclosed in U.S. Pat. No. 5,654,392, at col. 24, 1.9-15: “Non limiting examples of additives which may be used with rigid-rod or segmented rigid-rod polyphenylenes are: ( . . . ) carbon fibers, glass fibers, ( . . . ) and the like.” Fiber filled polyarylenes, while achieving the desired higher level of strength and stiffness as needed in certain demanding applications, still suffer from the same limitation in impact resistance as neat poly(aryl ether ketone)s; otherwise said, in such fiber filled polyarylenes, the fibrous reinforcing agent, while increasing profitably the stiffness up to the desired level, affects dramatically the impact resistance, causing it to decrease by about one and a half times. Besides, fiber-filled polyarylenes, likewise neat polyarylenes, suffer from several other important limitations: they have no ductile break, they are difficultly processed at the molten state and they have a somewhat lower thermal stability and chemical resistance than poly(aryletherketone)s.
In certain still more demanding applications where articles are used under stress at high temperature, a still more complex problem needs to be solved: in addition to gaining in strength, stiffness and impact resistance, the composition of matter of which the articles are made should further exhibit a higher heat deflection temperature than that of neat poly(aryl ether ketone)s. While fiber-reinforced poly(aryl ether ketone)s meet fully, and even exceed by far, this additional requirement, the use of neat or filled polyarylenes results in a slight to moderate increase of the heat deflection temperature when compared to that of neat poly(aryl ether ketone)s, which may be sometimes sufficient, sometimes not.
In the light of the above, there remains a strong need for materials offering a superior balance of properties, including:                a very high strength [higher than that of neat poly(aryletherketone)s]        a very high stiffness [higher than that of neat poly(aryletherketone)s and neat polyarylenes]; and        a very high impact resistance, as characterized by a standard notched IZOD test [higher than that of neat or fiber-reinforced poly(aryl ether ketone)s and fiber-reinforced polyarylenes].        
Desirably, the material should further exhibit:                a ductile break;        a good melt processability (better than that of neat or fiber-reinforced polyarylenes);        a high thermal stability (higher than that of neat or fiber-reinforced polyarylenes); and        a high chemical resistance (higher than that of neat or fiber-reinforced polyarylenes).        
Also, for certain very demanding applications where articles are used under stress at high temperature, the materials should preferably further exhibit a substantially higher heat deflection temperature than that of neat poly(aryl ether ketone)s and neat or fiber-reinforced polyarylenes.
Polymer blends have been widely taught and employed in the art. As broad as this statement may be, the blending of polymers remains an empirical art and the selection of polymers for a blend giving special properties is, in the main, an Edisonian-like choice. In the field of miscibility or compatibility of polymer blends, the art has found predictability to be unattainable, even though considerable work on the matter has been done. According to authorities, “It is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility and even partial miscibility is the exception. Since most thermoplastic polymers are immiscible in other thermoplastic polymers, the discovery of a homogeneous mixture or partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently unpredictable with any degree of certainty, for example, see P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, Chapter 13, page 555.” The miscibility or compatibility of polymer blends is even more also unpredictible when additives such as fibers are incorporated to the polymer blends.
Example 13 of U.S. Pat. No. 5,654,392 (same as above cited) is a prophetic description of a manufacture of a composite material by a pultrusion process involving a polyaryletherketone (more precisely, a polyetheretherketone) at molten state, and a polyarylene (more precisely, a rigid-rod polyphenylene) in the particular form of fibers. By giving credit to a pultrusion process which requires contacting, during a significant amount of time, polyarylene fibers having a Tg as low as about 160° C. with molten polyaryletherketone (i.e. at a temperature above about 340° C.) without affecting the fibrous nature of the polyarylene fibers, US '392 gives thereby credit to the incompatibility and the inmiscibility of polyarylenes with poly(aryletherketone)s, discarding thereby the skilled person from mixing polyarylenes with a poly(aryletherketone)s in a significant amount so as to obtain valuable physical blends, since, in such a case, the expectation would be great to obtain unstable ones, highly subject to phase separation.